Propellium atmospheres.

[Samniss Arandeen]

On Kerbin and Laythe, there's enough oxygen in the atmosphere to combust liquid fuel without the aid of an oxidizer. Jet engines were invented to scoop this atmosphere and use it to combust fuel to generate thrust.

However, there should be other bodies that have the inverse situation. I imagine Eve in particular having an atmosphere rich in Propellium. What this means is that, with a specially designed engine, no liquid fuel is required! Instead, this engine takes in the air and burns it with the aid of oxidizer. Certainly would make Eve exploration significantly easier; though, it's nowhere near powerful enough for an Eve SSTO.

[LABHOUSE]

Good idea but maybe change the name of liquid fuel to methane or have it in parentheses to make it have more sense as that is in most atmospheres some more than others (will fuel mars colonial transporter)

[AlexanderB]

Jet engines leaving a soot-trail like an old steamtrain.

[r4pt0r]

like specially designed eve atmo jet engines? now that would make things...interesting. I'd say make them 1/4 the strength of the standard jet engine. cant have it getting too easy.

[Red Iron Crown]

Eve is supposed to be difficult to return from, it's one of the game's biggest challenges. I'm not sure an engine that makes it much easier is desirable in the stock game.

Eve exploration itself is borderline trivial as long as you don't mind transmitting your results. It is the easiest celestial body to land on.

[r4pt0r]

That's a very true point, I can only imagine the outcry were such an OP engine to come out. I thought the ARM parts debate was bad...

[Kasuha]

From realistic point of view, there's no way an airplane jet engine would work in atmosphere of kerosene vapors trying to burn oxygen. So while it is theoretically possible, it would require completely different engine. That would mean we would get a part that is only useful on one planet which is not Kerbin. Not very practical in my opinion.

Another question is whether there is chance for burnable atmosphere on Eve. It's a game so we may give it any atmosphere we want. But for instance Venus has definitely non-burnable atmosphere and the same for Mars. Even Earth would have similar atmosphere to these two if there were not living organisms converting CO2 to O2.

[SiliconPyro]

Such an engine would be particularly interesting in the atmosphere of, say, Jool. No chance of your landing, but maybe a more efficient way of putting around the atmosphere collecting science. If the engine were only useful there, but did add capability, it would have some benefit, even if it were mostly a novelty.

[peadar1987]

There was a thread about a similar thing a while back, alternative oxidisers or something it was called, although it came at the problem from another direction.

In terms of running an engine, there's no functional difference between supplying oxidiser or supplying fuel, so long as the two are roughly the same molecular mass.

It would certainly be interesting if we assume that Jool has a hydrogen-rich atmosphere like Jupiter. In theory, it would probably be possible to run a jet engine in Jupiter's atmosphere by providing oxidiser. Although without biomes, the point of a jet aircraft is pretty limited.

[SiliconPyro]

There was a thread about a similar thing a while back, alternative oxidisers or something it was called, although it came at the problem from another direction.

In terms of running an engine, there's no functional difference between supplying oxidiser or supplying fuel, so long as the two are roughly the same molecular mass.

It would certainly be interesting if we assume that Jool has a hydrogen-rich atmosphere like Jupiter. In theory, it would probably be possible to run a jet engine in Jupiter's atmosphere by providing oxidiser. Although without biomes, the point of a jet aircraft is pretty limited.

The problem is that, by volume, you need a lot more oxidizer to run an engine, so you're barely better off than a closed cycle rocket.

As you mentioned, unless there are maybe gas pocket biomes or something, the entire endeavor would be just for the sake of saying you did it. Completely fruitless.

[Engineer of Stuff]

Good idea!

[Engineer of Stuff]

So we could blow up Jool. Funny.

[peadar1987]

The problem is that, by volume, you need a lot more oxidizer to run an engine, so you're barely better off than a closed cycle rocket.

As you mentioned, unless there are maybe gas pocket biomes or something, the entire endeavor would be just for the sake of saying you did it. Completely fruitless.

For combining hydrogen and oxygen, you need twice as much oxygen as hydrogen, which is better than, say, Kerosene, which combines with 16.5 parts oxygen.

Mass-wise, yes, most of the mass is going to be oxygen, but, as I think Ferram has pointed out before, the main benefit of a jet engine isn't actually that you don't have to carry half of the reactants, the benefit is that you don't have to carry a huge amount of the reaction mass. This is what makes them so much more fuel efficient. You don't need to have a stoichiometric amount of oxidiser, you can react it with some proportion of the intake hydrogen to run a high-bypass turbofan engine, and greatly increase your fuel efficiency that way (although, as you rightly pointed out, not nearly as much as running it the other way round, by carrying fuel in an oxidiser-rich environment)

[SiliconPyro]

I said volume when I meant mass. I feel dumb now.

[wizzlebippi]

You would be far better off with an electric ducted fan, assuming your craft has the ability to generate enough electricity.

[Kasuha]

Electrical propellers would be incredibly cool even if they only provided small thrust (in real life even combustion-driven propellers can't compare to jets, the less propellers powered by solar energy). And sure enough they'd provide solution for all atmospheres.

[wizzlebippi]

I didn't say propeller, I said ducted fan. A modern multi-stage turbofan engine has a core that produces all the energy to drive the main fan. The majority of thrust comes from the fan, not the core. It probably won't get you supersonic, but it will keep you flying.

[Red Iron Crown]

An electric ducted fan is incredibly similar to a cowled electric propeller, if there is any difference at all.

[peadar1987]

Yeah, a high-bypass turbofan is basically a ducted propeller driven by a gas turbine. Using the gas turbine's exhaust to increase thrust is a bonus, but you don't actually gain that much. So an electric turbofan using a nuclear reactor or battery to power it would have similar thrust to a comparable kerosene-driven one.

[wizzlebippi]

Propellers and ducted fans are very different, mainly that flow over ducted fans are mostly 2D because the duct prevents the formation of tip vortices. This allows thrust to increase linearly from the hub outward. Also, next time you see an airliner, look at the shape of the bypass duct. It widens from the inlet to the fan, slowing air and increasing static pressure, in turn increasing thrust.

[Kasuha]

I think it's irrelevant if it is ducted fan or propeller, real-life efficiency does not quite translate to the game efficiency, I'm certain it would get about the right thrust to be fun.

[wizzlebippi]

I know, but I hate to let misconceptions stand.